The first I remember hearing a Robin singing drop used much was after they recorded her during a break singing along with "Cocaine" a few years ago. Her first singing drop was taken years from a song she was singing for Stuttering John's CD where they isolated her vocals ("somebody gotta kill the FCC"). I guess in the last year or so they started asking her to sing the top 5 songs for a bit and they've cut a few drops out of those. Those are the drops you hear now. She was always embarrassed of her voice before then, now she seems fine with it.

Gary's played his trumpet since the Losers band was around, but the current drops come from Gary trying to play his trumpet along with Robin's recording of a Guatemalan marching band (aka Robin's news theme for the last few years). I think he attempted to play the trumpet along for a bit for Robin's birthday several years ago. It seems like a musician had instructed him on what keys to hit.

The origin is they need non-offensive drops (no more porn whores gagging on cock) so they asked Robin to sing some Whitney Houston songs and Gary, who thinks he's the guru of rock and pop music, to play an instrument